Re: [Qemu-devel] [PATCH] ppc64: fix compressed dump with pseries kernel

[David Gibson <david@gibson.dropbear.id.au>]

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On Wed, Aug 03, 2016 at 09:55:07PM +0200, Laurent Vivier wrote:
> If we don't provide the page size in target-ppc:cpu_get_dump_info(),
> the default one (TARGET_PAGE_SIZE, 4KB) is used to create
> the compressed dump. It works fine with Macintosh, but not with
> pseries as the kernel default page size is 64KB.
> 
> Without this patch, if we generate a compressed dump in the QEMU monitor:
> 
>     (qemu) dump-guest-memory -z qemu.dump
> 
> This dump cannot be read by crash:
> 
>     # crash vmlinux qemu.dump
>     ...
>     WARNING: cannot translate vmemmap kernel virtual addresses:
>              commands requiring page structure contents will fail
>     ...
> 
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>
> ---
>  target-ppc/arch_dump.c | 5 +++++
>  1 file changed, 5 insertions(+)

Urgh.. so, really the page size used by the guest kernel is a
guest-side detail, and it's certainly possible to build a 4kiB page
guest kernel, although 64kiB is the norm.

This might be the best we can do, but it'd be nice if we could probe
or otherwise avoid relying on this assumption about the guest kernel.

> 
> diff --git a/target-ppc/arch_dump.c b/target-ppc/arch_dump.c
> index df1fd8c..ad37a59 100644
> --- a/target-ppc/arch_dump.c
> +++ b/target-ppc/arch_dump.c
> @@ -220,6 +220,11 @@ int cpu_get_dump_info(ArchDumpInfo *info,
>      } else {
>          info->d_endian = ELFDATA2LSB;
>      }
> +    /* 64KB is the page size default for pseries kernel */
> +    if (strncmp(object_get_typename(qdev_get_machine()),
> +                "pseries-", 8) == 0) {
> +        info->page_size = (1U << 16);
> +    }
>  
>      return 0;
>  }

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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